Identification of substrate proteins for cathepsin L that are selectively hydrolyzed during the differentiation of imaginal discs of Sarcophaga peregrina

Previously, we showed that cathepsin L is essential for the differentiation of imaginal discs of the flesh fly [Homma, K. & Natori, S. (1994) J. Biol. Chem. 269, 15 258-15 264]. We have now identified imaginal disc proteins that are susceptible to digestion by cathepsin L and showed that they are selectively hydrolyzed during imaginal disc differentiation. Two of these proteins, with molecular masses of 210 and 200 kDa, were further characterized. Immunofluorescence studies suggested that they were intrinsic components of the basement membranes of various tissues. They were selectively hydrolyzed at the elongation stage of imaginal leg disc differentiation. Western blotting of embryos at various developmental stages showed that these proteins were only detected at the end of embryogenesis.